. The build up of toxic chemicals is another hotly debated subject especially in light of recent revelations from the Reefing DSB's founding father Dr. Ron Shimeck. 'Dr. Ron' as he is commonly known, has made recent reference to the 'possible' build up of heavy metals in the bed 'and other areas of our aquariums', via precipitation. And that any drastic drop in parameters such as Ph 'might' cause the release of these back into the water column with consequent damaging effects to our livestock. This is, 'I might add' an experiment still in progress which I eagerly await the outcome of, as the results might change the way we all view and approach the long-term husbandry of our charges. As for the conclusions, Dr Ron has already suggested that replacement of the media might be necessary every four to five years in an effort to rid the system of this build up, plus it may be stemmed from happening for longer periods via the use of 'Polyfilters' which are specially designed to deal with this type of impurity, ideally when preparing fresh salt mixes up prior to addition to the system. In this respect there 'might' end up being some argument in keeping DSB's in a detachable sump or one not unlike my design, ( DIY 4) So that when this type of maintenance is carried out, it will not damage the rest of the system with a sudden release of un-treated Amm, NO2, and NO3 that is being worked on in the sand layers at that time. If this truly is the case, then my only suggestion rather than starting from scratch each time, (which none of us can realistically afford), Would be to house the DSB in a separate sump which can be shut off from the rest of the system, and then replace 1/4 of the DSB every year to keep things at acceptable levels. Any pollution that is emitted from the bed will be kept away from the main tank, and can be simply changed by flushing the DSB through with some tank water prior to reattaching to the rest of the system. As for any other chemicals / gases that are part of the breakdown process. then I personally find it hard to believe that they could possibly accumulate to dangerous levels in a well maintained and well fed DSB. the mere fact that all the sand is being moved around so much, actually increases the possibly that any accumulated harmful chemicals are dispersed via diffusion before they get a chance to do any damage, to be removed via other methods such as skimming, Carbon or Polyfilters.
Everything seems settled right now 
no problems, my slight diatom problem is dying back for sure, hopefully when I clean the glass this time it wont grow back so bloody quick 
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